You will get "ambiguous between the action methods ".
when I call action method About using following url http://your applicationname/Index/ABOUT I got this server error

This means, The framework doesn't determine which "about" function to call, and throws the exception telling that the call is ambiguous. To fix this problem is to change the action name. If for some reason you don’t want to change the action name, and one of these function is not an action, then you can decorate this non action method with NonAction attribute.

Example:

[NonAction]publicActionResult aBOut()
{
return View();
}

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